1. Field of the Invention
The present invention relates to an apparatus for automatically adjusting a light axis or a lighting area of a light beam emitted from a vehicle headlight in the horizontal direction on the basis of a steering angle.
2. Description of Related Art
It is known to perform a swivel control on a vehicle headlight for adjusting horizontally the light beam emitted from the vehicle headlight in accordance with the steering angle of the steering wheel of the vehicle.
Generally, such a swivel control is enabled while the vehicle is traveling at a speed higher than a predetermined threshold speed. Accordingly, when the vehicle is stopped or the vehicle's speed falls below the threshold speed, the swivel control is disabled, so that the vehicle headlight is returned, irrespective of the steering angle at that time, to its initial angular position where the light axis of the vehicle headlight projects in the straight forward direction or initial direction. Such a case occurs when the vehicle is making a left or right turn at an intersection, for example. When the vehicle starts moving after it has stopped to make a left or right turn, and the vehicle speed exceeds the predetermined threshold speed, the swivel control is resumed. So, the light axis of the vehicle headlight may change abruptly from the initial direction to a swivel-controlled direction depending on the steering angle at that time. Such an abrupt change in the direction of the light axis of the vehicle headlight often causes the driver to feel awkwardness in the control of beam patterns.
It is also known to disable or halt the swivel control upon the satisfaction of the conditions that the steering angle is larger than a predetermined angle, that the vehicle speed is equal to or lower than a predetermined threshold speed, and that a turn indication signal indicative of a status (on or off) of a turn indicator of the vehicle is in the on state, and to enable or resume the swivel control upon the satisfaction of the conditions that the vehicle speed is higher than the predetermined threshold speed, and that the turn indication signal is in the off state. However, in such a prior art swivel control system, there is a problem in that the driver sometimes cannot benefit the effects of the swivel control for a relatively long period of time. One example is that the vehicle travels at a low speed along a road running alongside a railroad, makes a right turn to cross a railroad crossing keeping the low speed, and makes a second right turn to go into another road running alongside the same railroad. In this example, the swivel control is disabled until the vehicle finishes the second right turn.